1. Field of the Invention
This invention relates to a bidirectional buffer circuit and a signal level conversion circuit.
2. Background Art
In data transmission between electronic devices and between circuits, data transmitting and receiving are often performed alternately, and only one thereof is rarely performed. For example, in memory devices, stored data in a received address are transmitted to a sender in return. In this case, as the data transmitting and receiving are not often performed at the same time, bidirectional communication of transmitting and receiving the data is often performed with sharing one signal line. Thereby, the number of the signal lines can be small, and cost of the communication system can be easily reduced.
When the signal line becomes long, a buffer is required on the way of wiring. Moreover, in the electronic devices and in the circuits, each power voltage of them is not always the same. In the case of different power voltages, a level shifter is required to convert a signal level.
If there is no signal of the transmission direction in the buffer circuit or the level shifter corresponding to the bidirectional signal, a data transmission rate lowers. Using the directional signal, however, the buffer needs another long wire for the directional signal so that the cost increases. Moreover, the buffer circuit or the level shifter may provide an apparatus for determining either the transmitting or the receiving. However, such the apparatus complicates the buffer circuit and the level shifter, and therefore, the cost increases.
An example for a signal level conversion circuit is disclosed in JP-A 2005-176172 (Kokai). In this example, two serially connected inverters, inserted between an input buffer and an output buffer, reduces the number of another elements the stages to simplify its circuit structure. Moreover, the signal level conversion circuit reduces a chip size and a delay of the signal propagation.
However, also this disclosure example, the circuit becomes complex because of using a selective signal for switching the transmission direction of the signal and its structure becomes complex.